1. Field of the Invention
The present invention generally relates to devices for assisting the pumping action of the heart, and more particularly to an inflatable balloon to be placed within the heart itself.
2. Description of the Prior Art
Heart disease is the number one killer among persons over 30. The most common manifestation of this disease is heart attack, or myocardial infarction. A heart attack is usually caused by clogging of the coronary arteries, those vessels which supply oxygen and nutrients to the heart itself, often due to an excessive accumulation of lipid material (fat) within the arterial walls (coronary occlusion or thrombosis).
A milder heart attack may result in mere "heart failure," characterized by an inability of the heart to pump blood at the rate needed to maintain adequate blood flow throughout the body. In this scenario, blood flow through the coronary arteries is appreciably diminished, but not totally cut off. This results in decreased blood flow (ischemia) to localized portions of the muscular tissues of the heart, with possible necrosis. Inadequacy of the coronary blood supply may give rise to chest pains (angina pectoris), and lead to shortness of breath (dyspnea) and the accumulation of excessive fluids (edema) in the lungs, liver, and lower limbs. The heart reacts by pumping more forcibly and faster, but this typically causes the ventricles to grow larger and become flaccid. Although the volume of the ventricle is increased, the maximum pressure during the isovolumetric period is actually lowered.
In the past, devices have been invented to serve some of the needs of heart failure patients. One important medical tool devised to assist the failing heart is the intra-aortic, or intra-arterial, balloon (IAB). The IAB is usually inserted into the body via the femoral artery near the groin, and threaded up to the aorta. An early IAB is disclosed in U.S. Pat. No. 3,504,662, issued to R. Jones. That device provides a peristaltic pumping action. Another IAB, providing uni-directional pumping, is described in U.S. Pat. No. 3,692,018, issued to Goetz et al. The balloon may be placed in the ascending or descending portions of the aorta, and more than one balloon may be employed, as depicted in U.S. Pat. No. 4,527,549, issued to S. Gabbay.
Numerous other advances have occurred in IAB technology. U.S. Pat. No. 4,327,709, issued to Hanson et al. describes an apparatus for percutaneous introduction of an IAB through a dilator-sheath. Special features of the balloon have also been devised. For example, U.S. Pat. No. 4,346,698, also issued to Hansen et al., discloses an IAB which has a stylet therein for rotating the IAB so as to twist and thereby decrease the diameter of the IAB during insertion. Improvements on this idea are discussed in U.S. Pat. Nos. 4,402,307; 4,467,790; and 4,531,512.
Basically, the IAB is designed to inflate immediately upon the closing of the aortic valve, thereby expelling blood from the aorta into the connecting arteries. The synchronous timing of the balloon is controlled by electrical signals from the heart, i.e., by monitoring the EKG of the patient. The tip of the balloon may even be equipped with an electrode to provide this function, as shown in U.S. Pat. No. 4,552,127, issued to P. Schiff.
All of the above devices, however, suffer one critical disadvantage in that they take for granted that the heart will be able to force a sufficient amount of blood into the aorta in the first place. Where the efficiency of cardiac output is severely affected by myocardial stretching, systemic blood pressure can drop from 130/80 to as low as 50/30. In such cases, an intraaortic balloon is, at best, a band-aid remedy.
It would therefore be desirable and advantageous to devise an intraventricular balloon to assist the pumping action of the heart. No such device yet exists, although an article by Donald et al., published in the Journal of Thoracic and Cardiovascular Surgery, vol. 63, no. 5 (May 1972), discusses open heart experiments employing a cardiac balloon pump on a dog.